This invention relates to novel Al--Li--Zr alloys having high strength, high elastic modulus, low-density, good corrosion resistance and good ductility. Methods of forming these novel alloys are also disclosed.
Aluminum-lithium alloys containing up to 3.5 wt % lithium have been the subject of much research in recent years (Sanders, T. H., Jr., et al., eds. Aluminum-Lithium Alloys, TMS-AIME, Warrendale, PA (1981)). The interest in these alloys arises from the dramatic increase in elastic modulus and decrease in density associated with the addition of lithium to aluminum. In addition, with appropriate heat treatment, metastable .delta.' (Al.sub.3 Li) precipitate available in these alloys affords considerable strengthening. However, these alloys also exhibit low ductility and fracture toughness, which severely limits their commercial application.
A primary factor in the loss of toughness is slip localization which occurs as a result of work-softening on certain slip planes during deformation. The shearable nature of the .delta.' precipitate and consequent decreased resistance to dislocation slip on planes containing the sheared .delta.' is considered to be responsible for this behavior (Sanders, T. H., Jr., et al Acta Metall. 30, 927 (1982) and Sanders, T. H., Jr., Factors Influencing Fracture Toughness and Other Properties of Aluminum-Lithium Alloys, Naval Air Development Center (1979)).
It would therefore be desirable to have an Al--Li-base alloy which retains the superior characteristics of Al--Li alloys but also possesses high ductility and fracture toughness.